Wireless communication systems typically have a base station or access point from which radio signals are transmitted and propagate. These signals are then received by a mobile station, remote station, user station, etcetera (referred to herein collectively as station) allowing communication to proceed. Stations may be, for example, a computer with a wireless modem such as a notebook computer fitted with a wireless local area network (WLAN) card (referred to herein as a wireless notebook), mobile telephone or a wireless personal digital assistant.
Wireless communication systems typically provide two-way or duplex communication so that an access point can exchange data with or “talk” to a station, such as a wireless notebook, and the station can “talk” to the access point. In effect, there are two separate radio links by which these two signals travel, known respectively as the down-link and up-link.
Radio frequency (RF) signals can only propagate a certain distance before their power level is appreciably attenuated. For example, there is a distance from a transmission source (e.g., transmitting antenna) at which the RF signal level falls below a certain threshold and cannot be usefully received. The area around a network access point in which signals can be received is known as the coverage area and is sometimes referred to as a cell. When a station moves outside the coverage area signals cannot be received and communication is not possible. Accordingly it is often desirable to implement wireless systems that create as large a network coverage area as possible at minimum cost.
Recently, wireless communications have been combined with local area network (LAN) systems to provide wireless LAN (WLAN) configurations in which stations may be freely distributed throughout a workspace, e.g., an office building, and provided with high bandwidth data communications (such as on the order of 10 to 54 mega-bits per second (Mbps)) without a network cable attached to the stations. Accordingly, WLAN infrastructure has been designed for indoor pedestrian (ambulatory mobility) access over relatively short distances (e.g., on the order of 1-30 meters). It is a challenging problem to extend the coverage area of a WLAN system to provide high bandwidth coverage in outdoor public areas.
One technique which has been implemented to extend the coverage area of a network is by the use of a relay or repeater system. The relay is a system that receives, amplifies and re-transmits radio signals at a higher power level. By placing a relay on the edge of an area of coverage, the relay receives, amplifies and re-transmits the signals from a first coverage area to a second coverage area, thus extending the coverage area of the original signals. However, the use of repeaters in providing extended coverage areas is not without problems. One of the significant problems for repeaters is that of feedback (i.e., some signals from the transmitter are fed back to the receiver of the repeater) causing the system to oscillate.
Examples of prior attempts to provide extended coverage using relay systems are shown in U.S. Pat. No. 5,812,933, issued to Niki, and U.S. Pat. No. 4,849,963, issued to Kawano, the disclosures of which are incorporated herein by reference. The relay system of Niki relies upon the cellular protocols used therein, clearly defining when up-link and down-link transmissions can occur, to prevent oscillation caused by feedback. If a protocol allowing simultaneous up-link and down-link transmission, such as a carrier sense multiple access/collision avoidance (CSMA/CA) protocol were used, the system of Niki would experience an increased chance of oscillation. The relay system of Kawano uses different frequency bands in the up-link and down-link (isolation between these two signal paths is provided by the protocol) such that a duplexer network is used to separate up-link and down-link signals and provide sufficient isolation without oscillation. Accordingly, the foregoing relay system configurations are not well suited for use with respect to a wide variety of communications protocols, particularly those commonly used with respect to WLANs (e.g., those implementing CSMA/CA protocols and/or time division duplexing (TDD)).
Cellular systems have been adapted to carry data communications over wireless links of relatively long distances (e.g., 500 meters or more). However, such cellular systems have heretofore provided such data communications with data rates much lower than those expected using WLAN communications. For example, third generation (3G) cellular systems provide macrocell coverage areas, but with a relatively low bit rate of 2 Mbps.
Accordingly, there is a need for a system and method for providing relatively high bandwidth data communication in a large coverage area, such as a macrocell having a radius on the order of 500 meters or more. There is a further need for a system and method for extending a coverage area of WLAN infrastructure to provide WLAN data communication in a large coverage area.